Mustached bats, Pteronotus parnellii, emit a diverse array of structurally complex communications sounds (calls) as well as stereotypic echolocation pulses. Surprisingly, many auditory cortex neurons that were previously considered to be "highly specialized" for processing echolocation signals, especially those in the left hemisphere, respond equally well or better to calls. First, with continued support, the work proposed here will electrophysiologically characterize the nature and extent of the hemispheric lateralization for processing calls. This will be accomplished largely by simultaneously recording from both hemispheres while presenting the appropriate call and echolocation (pulse-echo pair) stimuli and mapping stimulus preference, at both the population and single cell levels. Second, this research will explore auditory processing beyond the level of the auditory cortex by recording auditory responses in the frontal cortex. Despite over twenty years of auditory cortical research, very little is known about auditory responses within the frontal cortex of any species. Frontal auditory (FA) responses can be dramatically different from those in the auditory cortex. The proposed work will fill this gap by characterizing and categorizing FA neurons in a quantitative manner. A variety of species-specific calls and basic acoustic patterns (e.g., frequency modulated sweeps, constant frequency tone and noise bursts) will be presented and neurophysiological data will be acquired under computer-control. The final thrust of this proposal is to examine the role(s) of intracortical interactions during short-term auditory processing. Inter-hemispheric interactions may create hemispheric lateralization and fronto-temporal interactions may modify responses of echolocation and call processing neurons. To examine this short-term regulation, auditory stimulation will be paired with electrical microstimulation and transient focal inactivation of neurons in the auditory cortex on one side, while recording responses of single cells in the auditory cortex on the opposite side. Specific parameters to examine include (1) peak response rate, (2) response latency, (3) response duration, (4) temporal response patterns, and (5) call preference of neurons. This research will bring us closer to understanding call processing at the cortical level in mammals, and the basic auditory mechanisms for perceiving speech sounds in humans. It can have an especially important bearing on understanding different types of cortical deafness such as progressive pure word deafness.